Perimeter Calculator
Find the perimeter of any common shape. Select the shape type, enter the dimensions, and this tool computes the perimeter instantly.
Understanding Perimeter Across Shapes
Perimeter measures the total length of a shape's boundary. For polygons, this means adding all the side lengths. A square with side 5 has perimeter 20 because 5 + 5 + 5 + 5 = 20. A rectangle with length 8 and width 3 has perimeter 22 because 8 + 3 + 8 + 3 = 22.
Triangles follow the same logic. An equilateral triangle with side 6 has perimeter 18. A scalene triangle with sides 3, 4, and 5 has perimeter 12. The shape of the triangle does not matter; just sum the sides.
Circles are different. The perimeter is called circumference and uses the formula C = 2πr. Since a circle has no straight sides to measure, we rely on the relationship between the radius and the curved boundary. A circle with radius 5 has circumference approximately 31.42.
Practical Applications of Perimeter Calculations
Perimeter calculations help determine material needs for borders, fences, and trim. If you need to fence a rectangular yard that is 50 feet by 30 feet, the perimeter is 160 feet, so you need 160 feet of fencing.
In construction, perimeter defines the length of molding, edging, or framing material. A square room with 12-foot sides requires 48 feet of baseboard. A circular flower bed with a 4-foot radius needs about 25.13 feet of edging.
For running tracks and sports fields, perimeter determines the distance around the playing area. A standard running track lane is 400 meters, which is the perimeter of the path. Knowing perimeter helps with lap counting and distance measurement.
Perimeter vs. Area: What is the Difference?
Perimeter and area measure different properties. Perimeter is a linear measurement in units like meters, feet, or inches. It tells you how far you would walk around the outside of a shape.
Area measures the space inside a shape in square units. A square with side 5 has perimeter 20 but area 25. Doubling the side length to 10 doubles the perimeter to 40 but quadruples the area to 100.
This difference matters in real-world applications. If you are installing a fence, you care about perimeter. If you are laying sod or painting a floor, you care about area. Both measurements use the same input dimensions but answer different questions.
Frequently Asked Questions
What is perimeter?
Perimeter is the total distance around the outside of a shape. For polygons, add all the side lengths. For circles, the perimeter is called the circumference.
How do I find the perimeter of a rectangle?
Add the lengths of all four sides. Since opposite sides are equal, the formula is P = 2(l + w), where l is length and w is width.
What is the perimeter formula for a square?
Multiply the side length by four: P = 4s. All four sides are equal, so perimeter is four times one side.
How do I calculate the perimeter of a triangle?
Add all three sides: P = a + b + c. The triangle can be scalene, isosceles, or equilateral—the formula is the same.
What is the perimeter of a circle called?
The perimeter of a circle is called the circumference. The formula is C = 2πr, where r is the radius.